1998 f150 auto,4.6,2wd, 113000 miles. Truck is in exceptional shape been very well kept up. I do have some random odd brake issues. In advance all pads and rotors have been changed and resurfaced. In the morning upon initial start up and backing out of the drive way, while lightly touching the brake pedal for the first time of the day I feel a small undulation or pressure change in the brake pedal, it also makes a small groning sound. The sound and pedal feeling is very quick and momentary. It goes away and doesn't reappear until the next morning on first start up. Also the truck has odd symptoms though minor...like the pressure it takes to come to a complete stop sometimes drastically changes. One time X amount of pedal pressure will bring the truck to a nice gradual stop while another time the same X amount of pressure will make it feel like you've slammed on the brakes. On top of those 2 symptoms the brakes do shake or shudder like a rotor is warped, but doesn't shake/shudder consistently it does it under random braking pressure, at random speeds. As I said the fluid is full, the pads and rotors are solid. Could the master cylinder,ABS sensor or system be malfunctioning but not throwing a pcm code?

After a day or two of sitting, when I first set the brakes on my 98 it will sometime almost lock up when you first push the brakes. It goes away after the initial hard braking. It has done it since day one. I have checked all the brakes, the booster, vacuum and etc. I found that the rear antilock was the problem. I decided not to fix anything, since after reading a TSB on rear brake problems, that Ford says the rear controller will hang up when first applied. The TSB didn't give a repair, only saying to clean all the connections and all the sensors.

When it is time to replace the rear brakes, I'll change the whole axle out and put in the bigger 9.75 with disc brakes rear axle. At least that is my plan. I bought the correct axle assy and have it sitting for the right day. I also have the correct disc brake master cylinder and proportioning valve to make sure all is right and use the proper parts. (Disc and Drum use different m/cylinders and prop valves.) It has to be right the first time. If not..........crash.

It also depends if you have RABS or 4WABS. I personally have 4wheel ABS so I only need to change the master cylinder. As the ABS pumps are the same as the one with rear discs.

I wasn't going to go into all the intricacies of the switch, but you are correct. I have RABS so I do need the prop valve switch. I wouldn't with the 4w system. Ford has a different # for the prop on the f250 ld also.

97-99 was a nightmare working parts at Ford. Ford had 3 body designs, 3 different f250's, 2 diffent f150 (with the oversales of the 96's), and 2 f350 bodies. Nobody back then had serial numbers, so if the customer didn't know his exact body, we ran into problems for a while. All's well now tho. lol